In 2001, in this wind-whipped Sacramento River Delta town, 17 people in the town of about 4,500 lodged complaints with the council office about a strange odor brought about during the mid-afternoon by southeastern winds. They complained of flies and odor, said the town's then-Mayor Marci Coglianese.

"It made you feel energy-less," said Bob Tillisch, 58, a resident and retired U.S. Army chief engineer who first noticed the smell. A little digging revealed that a farmer upwind was applying a old load of biosolids, the term used by U.S. EPA to refer to treated sewage sludge.

"But smell is not a legitimate complaint," Tillisch said. "No one is tracking illnesses."

And that is the problem.

Phone calls about public health complaints come in at regular intervals to county health boards, city council offices, state departments of health or environment. Many places do not log the calls, and if they do, investigations into health complaints do not extend beyond a particular truckload of waste. Certainly no one is looking into whether applying sludge to the ground can have health effects.

And given the nature of the uncertainties involved and the bureaucracy that some researchers say exist within the industry, the answer to this question has remained hard to come by.

In 2002, the National Research Council called for better tracking of incoming health reports. In response, for eight years, EPA's money has flowed through an industry-affiliated group called the Water Environment Research Foundation (WERF) and has funded development of a generic surveillance protocol. WERF says it does not have current plans to implement these reports in any sort of health risk investigation related to biosolid application.

Nearly all scientists agree that sewage sludge can be beneficial if it is uncontaminated, as it is a rich source of phosphorus and nitrogen. It has two components -- bacteria naturally present in organic matter, which can be somewhat removed depending on how the sludge is processed; and heavy metals and chemicals such as any of the 11 flame retardants, 72 pharmaceuticals, 28 metals, 25 steroids and hormones, and others that EPA tested for in its 2009 national sludge survey. It can also contain chemicals that no one is looking for, any one of the 80,000 that are made in the United States.

The survey is, at some level, nothing more than numbers that can extend into rows and rows of chemicals present in sludge. They are all originally derived from wastewater from industries or homes, and no one knows what a particular quantity of some chemicals mean in terms of health effects. Many are a common part of daily lives, and people are exposed to them in larger quantities through other mediums.

Within soil, the way chemicals interact with ecology and wildlife, their accumulation within food webs and their persistence in the environment is unknown, according to Murray McBride, director of the Cornell Waste Management Institute at Cornell University.

"A lot of this is just gathering information to find out what this is going to say," said Connie Roberts, special assistant to the director of the water protection division for EPA's Region 4, which covers Alabama.

In Decatur, Ala., chemical companies released perfluorinated compounds (PFCs) -- the stuff that makes up nonstick cookware and has been linked to thyroid defects in pregnant women and to cancer in wastewater treatment plant workers -- into the sewage system over a period of decades.

The local wastewater treatment plant, Decatur Utilities, collected sludge, which was then sprayed onto grazing lands over a period of 12 years. Tests in 2009 showed that the fields -- a grazing ground for cattle -- contained PFOA and PFOS. Both chemicals are highly persistent in the environment and accumulate in the body.

Tests showed that other types of perfluorinated compounds were also present, but EPA does not have maximum safety limits for these, said Roberts. "We wouldn't participate if there wasn't some cause for concern," she said of continuing tests of water and people's blood in the region.